The present invention relates generally to explosive charges, particularly as employed in projectiles and the like, and more specifically to explosive charges having a shaped body of explosive for enhancing penetration of remotely located material. Remotely located material is defined as material located a distance of about 20 times the diameter of the explosive charge along an axis of symmetry of the explosive charge.
In a projectile explosive charge such as, for example, a rocket-launched or tube-launched projectile, armor piercing capability of a given quantity of explosive is substantially improved by shaping the forward portion of the charge to produce a cavity of appropriate size and shape. The cavity may conventionally be lined with a metal or metallic alloy which is collapsed and driven as a concentrated, fast moving jet of metal which is capable of penetrating remotely located monolithic steel to depths of as much as two to three times the diameter of the warhead. An especially advantageous cavity shape is a conical shape having an included angle of less than 90 degrees and preferably from about 42 to 60 degrees.
Shaped charges are conveniently formed by casting a mass of explosive in a casing, the end of which is closed off by a metallic, preferably copper, cone. The cone thus forms the conical forward cavity of the shaped charge. After the explosive has set, it is conventional to machine the rear end of the explosive material to adapt it to fit a rear body section and/or an explosive booster, primer or centering device.
During machining of the rear portion of the cast explosive material, adhesion between the explosive material and the casing is relied on to prevent turning of the explosive material in the casing. The applicant has discovered that the bond between the cast explosive material and the casing is frequently unsatisfactory to prevent rotation of the explosive material in the casing. Such rotation disrupts the symmetry of the explosive, particularly near the junction of the cone and the casing where the section of explosive is quite thin. In addition, slight asymmetries in either the cone or the body produce corresponding asymmetries in the explosive material cast thereupon. Such asymmetries are exaggerated when the explosive material is rotated away from its original location.
Even if the bond is sufficient to resist rotation of the explosive mass in the body, localized fracture of the explosive material may occur due to the stress applied therebetween during machining.
The penetration performance of the shaped charge depends critically upon symmetry of each of the elements about the axial center line thereof. Anything which disrupts the symmetry of the charge also influences the symmetry of liner collapse. If the liner does not collapse in a symmetrical fashion, then the corresponding jet will not be straight and its penetration capability against remote targets is degraded.
Prior attempts to improve the armor piercing performance of shaped charge warheads include changing the shape or density of the liner, improving the axial alignment of liner, explosive material and explosive initiator and increasing the diameter of the shaped charge. Changing the shape and/or increasing the density of the liner greatly increases the cost for the different material and requires new machinery for fabrication. Improved axial alignment implies a drastic improvement in machining and fabrication technology since current shaped charges already utilize tolerances near the limits of high production technology. Increasing the diameter of the shaped charge requires that the entire system for launch must be correspondingly increased and the weight of the larger warhead may make it unsuitable for lifting by military personnel.